This new volume focuses on a new, exciting field of research: Spintronics, the area also known as spin-based electronics. The ultimate aim of researchers in this area is to develop new devices that exploit the spin of an electron instead of, or in addition to, its electronic charge. In recent years many groups worldwide have devoted huge efforts to research of spintronic materials, from their technology through characterization to modeling. The resultant explosion of papers in this field and the solid scientific results achieved justify the publication of this volume. Its goal is to summarize the current level of understanding and to highlight some key results and milestones that have been achieved to date. Semiconductor spintronics is expected to lead to a new generation of transistors, lasers and integrated magnetic sensors that can be used to create ultra-low power, high-speed memory, logic and photonic devices. In addition, development of novel devices such as spin-polarized light emitters, spin field effect transistors, integrated sensors and high-temperature electronics is anticipated.